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    Augmentation of natural convection heat sink via using displacement design
    (2020-06-01)
    Abbas, Ali
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
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    Department of Mechanical Engineering
    Miniaturization of electronic devices demands an effective thermal management system for efficient cooling. Still, many electronic industries use natural convection cooling techniques like plate-fin heat sinks as far as no moving part (noise) and reliability is concerned. In this study, the widely-used plate fin heat sink is augmented by a novel fin displacement amid fin array. Yet the effect of fin displacement between alternate fins is experimentally and numerically investigated under natural convection condition. In the meantime, the effects of fin spacing, length, height, and heat flux on the heat sink performance subject to fin displacement is also studied. For the smaller fin pacing, introducing the fin displacement will delay the merging of boundary layers, and reduce the length of fully developed region accordingly. Smaller fin spacing can also entrain the outside air into the fin array at the upper portion of heat sink for offering additional enhancement. The fin displacement is especially effective for a smaller fin spacing. This is because fully developed flow prevails at a smaller fin spacing. On the other hand, the fin displacement may impair the performance when a very wide fin spacing is used. Similarly, the increase in the fin length also enhances the heat transfer performance under the fin displacement conditions. It is also found that the effect of fin height on the thermal performance is small and the effect of heat flux is negligible. The maximum reduction in the thermal resistance is 56% by adopting the displacement design. A drop in fin temperature at the upper portion with the displacement design may lead to a reduction in heat transfer coefficient. For the comparison containing the fixed volume, the heat sink with fin displacement offers a 30% heat transfer enhancement ratio, 28.7% reduction in total mass, and 27.4 % reduction in surface area when compared to the conventional heat sinks. (C) 2020 Elsevier Ltd. All rights reserved.
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    Experimental and numerical study on the performance of passive heat sink having alternating layout
    (2019-06-01)
    Chu, Wen-Xiao
    ;
    Lin, Yu-Chieh
    ;
    Chen, Ching-Yao
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    In this study, a novel passive heat sink with triangular fins having alternating layout to promote heat transfer performance of a passive heat sink is proposed and verified by experimental and numerical examinations. The heat sinks with rectangular fins (case A), triangular fins with right angle, 90 degrees (case B), triangular fins with right angle having alternating layout (case C), triangular fins with obtuse angle of 120 degrees (case D) and triangular fins with obtuse angle of 120 degrees having alternating layout (case E) are tested with vacuum pressure ranging from 400 Pa to atmosphere pressure. It is indicated that the triangular fin having alternating layout offer some benefits like entraining more airflow into the heat sink and a higher effective view factor, thereby showing an appreciable increase of effective heat transfer coefficient (HTC). Results obtained in low vacuum pressure show that the effective HTC of cases B, C, D and E can be improved by 1.5%, 5.5%, 3.0% and 12.1%, respectively as compared to the reference case A. Yet the effective HTC can be improved by 3.2%, 6.1%, 4.6% and 13.0%, respectively in atmosphere pressure. The numerical study is in line with the experimental results and the simulations suggest that the optimum angle of the proposed triangular fins having alternating layout can improve the effective HTC by up to 14.6% and 16.0% with obtuse angles of 150 degrees and 140 degrees when fin area is 2000 mm(2) and 3000 mm(2) , respectively. The benefits of triangular fins having alternating layout show even more superior performance when the heat sink is placed vertically and the effective heat transfer coefficient for triangular fins having alternating layout with 150 degrees is improved by up to 20.3%. (C) 2019 Elsevier Ltd. All rights reserved.
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    Analytical and Experimental Verification of Interleaved Trapezoidal Heat Sink
    (2017-01-01)
    Chen, Hong-Long
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    The objective of this paper is to explore the technique for lowering the contraction and hydraulic developing region pressure drop, in order to gain more airflow for electronic cooling heat sink for the same footprint and fin number. By combining two different geometrical perimeter shapes of fins, odd number is rectangular shape, and even number is trapezoidal shape, this new fin module design gains extra 10% airflow with little loss or equivalent thermal performance. Current data center server is suffering from too little airflow to cool essential chips due to enormous flow impedance for packing too many components inside. This technology is the solution to resolve this bottleneck. The precious extra 10% more airflow not only cools CPU chip itself; but also quite beneficial to cool other heating components inside servers. Also, this new design excels in low velocity of 2 m/s for thermal performance compared to original design. Lower velocity is equal to lower RPM of fan that leads to the advantage of energy saving.
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    Analysis and experimental verification of weight saving with trapezoidal base heat sink
    (2018-03-05)
    Chen, Hong-Long
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    A quick weight saving methodology with trapezoidal base heat sink applicable for electronic cooling application is studied analytically, numerically, and experimentally. The conventional heat sink with rectangular base can be modified into trapezoidal base for material saving. A differential equation capable of describing the temperature distribution of the trapezoidal base is derived and its closed-form analytic expression is derived. It is found that three parameters r(A) (ratio of effective surface area to the base area), r(d) (ratio of chip lateral length to the base length) and h(+) (modified convection heat transfer coefficient) play pivotal roles in balancing the material saving and the performance loss. When r(d) = 0.1, the material saving for r(t) = 0.6 is about 18%; while the corresponding performance loss is 2.93%. When r(d) = 0.2, the material saving for r(t) = 0.6 is about 16%; while the corresponding performance loss is 2.47%. The analytical results are verified with experiments with good agreement. (C) 2017 Elsevier Ltd. All rights reserved.
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    Analytical analysis and experimental verification of interleaved parallelogram heat sink
    (2017-02-05)
    Chen, Hong-Long
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    In this study, a novel air-cooled heat sink profile is proposed to compete with the conventional design. The new design is termed as IPFM (Interleaved Parallelogram Fin Module) which features two different geometrical perimeter shapes of fins. This new design not only gains the advantage of lower pressure drop for power saving; but also gains a material saving for less fin surface area. An assessment of flow impedance and performance between the conventional and IPFM heat sink is analytically investigated and experimentally verified. A new modified dimensionless friction factor for triangular region is proposed. The analytical predictions agree with experimental measurements for both conventional and IPFM design. In electronic cooling design, especially for cloud server air-cooled heat sink design, the flow pattern is usually laminar with Reynolds number being operated less than 2000. In this regime, the IPFM design shows 8-12% less of surface than conventional design when the flow rate is less than 10 CFM; yet the thermal performance is slightly inferior to the conventional design when the flowrate is raised towards 25 CFM. Yet in the test range of 5-25 CFM, a 10-15% lower flow impedance is observed. The smaller fin spacing, the more conspicuous reduction of flow impedance is observed. The optimization of cutting angle is around 35 degrees for 10 CFM, and it is reduced to 15 degrees at a larger flowrate of 20 CFM. (C) 2016 Elsevier Ltd. All rights reserved.
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    Performance improvement of high power liquid-cooled heat sink via non-uniform metal foam arrangement
    (2015-08-05)
    Chen, Kuan-Cheng
    ;
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    The present study proposes a novel concept by employing non-uniform arrangements of metal foams alongside the heat sink applicable for liquid cooling. A total of 7 arrangements by varying PPI (pores per inch) of metal foam are made and additional 4 multiple channel designs are fabricated for comparison. Test results indicate that non-linearity term in Forchheimer equation rises significantly with increase of PPI (or with the decrease of permeability). The results suggest that the transition from the linear Darcy regime to the quadratic Forchheimer regime depends on the metal foam structure. It is also found that metal foam appreciably outperforms conventional multiple channel heat sink. The thermal resistance can be reduced by more than 62% as compared to that of empty plate design. For a given pumping power, the non-uniform arrangement of metal foam shows the best performance by employing a larger PPI metal foam at the inlet, followed by a smaller PPI metal foam, and the least PPI metal foam should be placed at the rear part of the heat sink. (C) 2015 Elsevier Ltd. All rights reserved.
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    ON THE HEAT TRANSFER CHARACTERISTICS OF HIGHLY COMPACT HEAT SINKS
    (2011)
    Wang, Chi-Chuan
    ;
    機械工程學系
    ;
    Department of Mechanical Engineering
    This study conducts an experimental study concerning the airside performance of highly compact heat sinks under cross flow condition. The test fin patterns can be classified into four categories, namely the base plain fin heat sink (Type I), interrupted fin geometry (Type II), dense vortex generator (Type III), loose vortex generator (Type IV) and their combinations. It is found that the heat transfer performance is strongly related to the arrangement of enhancements. The interrupted and dense vortex generator configurations normally contribute more pressure drop penalty than improvements of heat transfer. This deterioration becomes especially evident at a lower frontal velocity. The oblique VG with cannelure structure shows an appreciable lower pressure drop than that of plain fin geometry. In the meantime, the presence of interrupted surface may also jeopardize heat conduction path due to constriction. The results indicate that the vortex generators operated at a higher frontal velocity is more beneficial than that of plain fin geometry. In summary of the test results, it is therefore concluded that augmentation via various fin patterns like interrupted or vortex generator is quite effective only at developing region. However, the conventional enhanced fin patterns lose its superiority at the fully developed region. To tackle this problem, some techniques employing swing flow or unstable flow field accompanied with the asymmetric design, shows potential to resolve this problem.